Labels, tapes and similar constructions are ubiquitous in modern society. Many such constructions include a release liner coated with adhesive, such as a pressure-sensitive adhesive (PSA), which is laminated to a paper or film face stock. Removal of the release liner allows the construction--face stock coated with adhesive --to be adhered to a substrate. The face stock and liner are a major cost of the label.
Many adhesives, such as those commonly used in label constructions, are not water dispersible or repulpable. Therefore, they make recycling of the label product difficult, due to the tendency of the adhesives to form globules during the repulping process. In addition, most PSAs are tacky when dry and cannot readily be used with ink jet printers that have become so popular in today's world. Moreover, such PSAs typically are not hydrophilic, making it difficult to print on them directly with water-based ink jet printer inks. Instead, only the face stock or liner is ink-receptive. The unsuitability of such PSAs for use in ink jet printers is compounded by the tendency of the adhesives to block the printer ports in the printers.
Although attempts have been made to formulate moisture activated or water activated adhesives, many of the adhesives produced have been rubber based and, therefore, subject to oxidative and UV degradation. Many rubber-based and other adhesives have been solvent borne, and thus objectional for environmental, health and safety reasons. The following patents are representative. U.S. Pat. No. 3,681,179 to Theissen discloses a solar control film construction having a water-activatable adhesive system comprising a normally tacky and pressure-sensitive adhesive coating covered by a thin, tack-free continuous water-soluble layer. A tack free emulsion acrylic adhesive is not disclosed.
European Patents Nos. 199,468 and 297,451 describe a method for compounding water-activatable hot melt adhesives comprising polyaklylenimine or other vinyl heterocyclic monomers, a hydroxy-substituted organic compound, a plastizier, tackifier, and filler, and an antioxidant. No mention is made of making water activatable emulsion acrylic adhesives.
U.S. Pat. Nos. 4,331,576 and 4,325,581 to Colon et al. disclose common water-soluble hot melt adhesives based on polymers containing vinyl pyrrolidone and other heterocyclic monomers. Emulsion acrylics are not disclosed.
U.S. Pat. Nos. 4,052,368 to Morrison and 4,172,824 to Harrington describe water sensitive hot melt adhesives including polyester-based adhesives which typically comprise a copolyester in combination with a plasticizer. The systems are not emulsion acrylics.
None of the above-identified patents disclose or suggest the possibility of making a hydrophilic, acrylic emulsion polymer that is non-tacky when dry and water-activatable to become an adhesive, and that can be used in a "label-less" or "liner-less" construction, i.e., a construction in which either a face stock or a liner is not required.